The invention relates to a method for processing source sound for therein enhancing wanted sound with respect to unwanted sound, said method comprising the steps of:
distributing said source sound over a plurality of bandpass filters in as many channel in parallel; PA0 in each channel applying a respective filter means for preferentially filtering the wanted sound with respect to the unwanted sound in that channel's frequency band; PA0 aggregating output signals of said channels to an enhanced output sound. PA0 feeding each bandpass filter's output to an envelope detecting means to feed that channel's filter means; PA0 feeding each respective filter means' output to an envelope modulating means to generate that channel's output signal. PA0 bandpass filter means at a frequency of the associated channel; PA0 envelope detecting means fed by the channel's bandpass filter means; PA0 comb filter means fed by the channel's envelope detecting means fed by the channel's; PA0 envelope modulating means fed by the channel's filter means;
First, the wanted sound may be speech, or more generally, such sound to which a particular pitch may be attributed. Sound having no such pitch is left out of consideration as a target for being enhanced. Now, sound enhancing is improving the signal-to-noise ratio, wherein the noise may be another sound or voice than the one to be enhanced, music, noises generated by identifiable objects such as machines, or just physically present noise, of which the source is unknown or indistinct. Such enhancing intends to make the wanted sound better comprehensible, more agreeable or otherwise more suitable. It would be feasible to enhance the sound of a particular musical instrument with respect to other instruments. The result of the enhancing may be used per se. Another application would be to subtract the enhanced signal from the source signal for subsequently using or further processing of the subtraction result.
The described straightforward method may succeed for low frequencies that are coupled to the pitch of the signal in question, whether wanted or unwanted. Higher harmonics, however, cause problems of various nature. First, the phase of such higher harmonics is less precisely coupled to the basic pitch period; in extreme cases, the phase itself is subject to noisy phenomena. Therefore, such methods would attribute to these latter noisy phenomena a certain harmonic structure. This would, in its turn, cause disturbances in the higher frequency range of the wanted signal, and effectively attenuate higher-frequency components thereof. This effectively would render the recited solution imperfect with respect to the objects recited supra.